Known light emitting diode (LED) lighting units include LEDs mounted on a heat sink and enclosed by a lens. The lens protects the LEDs and circuitry and may provide desired optical characteristics such as light diffusion. For example, if the LED lighting unit is designed to replace a conventional fluorescent bulb, LEDs are known to be mounted on a heatsink that is encircled with a cylindrical lens, such as disclosed in U.S. Pat. No. 7,049,761.